Microstructural investigation of Sn nanoclusters in double-energy implanted and annealed SiO2 layers with cross-sectional TEM

500 nm SiO2 layers were implanted with 350 and 700 keV Sn ions at room temperature to study the formation of nanoclustering within the insulating layer with cross-sectional TEM. Ion energy and fluence were adjusted to achieve an almost constant Sn concentration of about 1.25 and 2.5 at.% in the SiO2 layer, respectively, as measured with RES. After a subsequent annealing treatment for 30 min in dry N-2 ambient, three different kinds of regions of nanoclusters appear in the insulating layer at temperatures above 600 degrees C. Close to the surface of the specimens a nanocluster band is observed, which is related to in-diffusion of moisture from the surrounding ambient during annealing. That results in the formation of crystalline SnOx clusters (typical size 2-5 nm). Similar effects occurred for comparable Ge implantations. Following the cluster band close to the surface another region of clusters appears in the micrographs. However, these crystalline Sn clusters are significantly larger up to 60 nm and, in addition, their mean distance is relatively far from each other. In a distance of less than 10 nm away from the SiO2/Si interface, a third but very narrow Sn nanocluster band appears, well separated from the interface. This band is directly related to the irradiation damage formed by recoils in that region during implantation. In this contribution, the influence of the fluence and annealing temperature on the nanoclustering is presented. (C) 1999 Elsevier Science B.V. All rights reserved.